The invention generally relates to a technique and apparatus for multiple zone perforating.
A typical subterranean well includes multiple production zones. In the production of well fluid from these zones, the well fluid from the zones may be commingled; or alternatively, the zones may be isolated and produced separately. For the latter type of production, the zones may be initially isolated with packers and then perforated to prepare the zones for production.
Conventional systems to produce from multiple isolated zones use multiple strings to regulate and/or shut off the flows from the zones. As a more specific example, FIG. 1 depicts a conventional system 5 for completing and producing well fluid from two isolated production zones. As depicted in FIG. 1, a production string 10 (often called the “long string”) extends into the interior of a casing string 8 of the well. During production from the well, the production string 10 communicates fluid from a lower production zone (not depicted in FIG. 1) that is located below a lower packer 16 to the surface of the well. The system 5 also includes another production string 12 (often called the “short string”) that extends into the well beside the production string 10 and into an upper production zone 15 that is isolated between an upper packer 14 and the lower packer 16. Therefore, as depicted in FIG. 1, both production strings 10 and 12 extend through the upper packer 14.
Unlike the production string 10, the production string 12 does not extend through the packer 16. Instead, the production string 12 has a lower end 30 to receive well fluid from the production zone 15. As depicted in FIG. 1, the production string 12 may include a flow control device 32 for purposes of regulating and/or shutting off flow from zone 15.
For purposes of preparing the zone 15 for production, the well casing 8 and surrounding formation inside the zone typically are perforated using a perforating gun 22 that is eccentric to and clamped to the production string 10. More specifically, the production string 10 may include a Y-block gun hanger 20 for purposes of hanging the perforating gun 22 below the hanger 20, and the hanger 20 may include blast joints (larger outside diameter tubing) to protect the integrity of the production string 10. The perforating gun 22 extends beside and is coupled to (via clamps, such as a depicted clamp 23) section 25 of the production string 10. The production string 10 may include a guide nose 26 for purposes of connecting the perforating gun 22 and guiding the perforating gun 22 into the well.
A potential drawback with the system 5 is that the size of the perforating gun 22 is limited. More particularly, as can be seen from FIG. 1, inside the zone 15, the production string section 25 and perforating gun 22 span across the interior diameter of the casing string 8, thereby restricting the overall available outer diameter for the perforating gun 22. Another potential drawback with the system 5 is that the perforating gun 22 does not produce perforations that extend completely around the casing string 8. The limited perforating angle is due to the fact that the perforating charges of the gun 22 are directed away from section 25 of the production string 10 for purposes of avoiding damage to the production section 25. Therefore, the fluid carrying section 25 resides in a wedge that is excluded from the perforating charge phasing pattern of the perforating gun 22.
Thus, there exists a continuing need for a perforating/completion system that addresses one or more of the problems that are set forth above as well as potentially addresses one or more problems that are not set forth above.